Interference is one of the main factors that restrict the capacity of a wireless communication system. Taking a cellular system as an example, although the impact caused by interference may be relieved through resource allocation and power control, the interference between cells is still a main factor that restricts the capacity of a cellular system.
A main solution for suppressing the interference between cells is to eliminate interference through synergetic operation of multiple adjacent cells. In the downlink direction, interference can be eliminated by a pre-coding technology through synergetic operation of multiple adjacent cells. One mode of interference elimination is: Adjacent cells completely share the data of the mobile terminal users that interfere with each other, but Base Stations (BSs) need to be interconnected through high-speed and large-bandwidth links, which are costly in a practical system. In the uplink direction, each mobile terminal is completely independent. One mode of interference elimination is: Data is received jointly between the BSs, and the interference between users is eliminated through joint detection, and the signals of each user are separated out. This mode of interference elimination requires larger bandwidth than the mode of sharing the data to be sent in the downlink direction, and also leads to high costs in a practical system.
For uplink or downlink direction, eliminating interference between cells without sharing the data to be transmitted is the most cost-efficient and practicable solution to the operator. Besides, if a relay station is employed, because no direct interconnection link exists between relay stations, the suppression of the interference between relay stations also requires the technology of eliminating interference without sharing the data to be transmitted. In practice, all such problems may be summarized as interference elimination of a K-user Multiple Input Multiple Output (MIMO) interference channel model. In a K-user interference channel model, the number of the transmitting sources and the number of users are K; the number of antennas of each transmitting source is M, the number of receiving antennas of each user is N, and no data is shared between the transmitting sources, and no data is shared between the users, namely, each transmitter knows data of only its own user (or receiver) but does not know data of other users (or receivers). Therefore, each transmitter can perform interference suppression between users only through pre-coding for data of its own users.
Interference alignment is a main technical solution for eliminating interference in the K-user interference channel model. Its basic conception is that the interference vectors received by user i (namely, the user numbered i) from other transmitters are as aligned as possible, thus obtaining the minimum possible interference space and eliminating interference. However, the research on the linear interference alignment technology is still in the initial stage, and the effective interference alignment for any number of users and any number of antennas is still pending.